silt up vs back up

silt up and back up both are verbs.

Word	Noun	Adjective	Verb	Adverb
silt up	No	No	Yes	No
back up	No	No	Yes	No

As verbs, back up is a hypernym of silt up; that is, back up is a word with a broader meaning than silt up:

Other hypernyms of silt up include choke, choke off, clog, clog up, congest, crap up, foul.

silt up (verb)	back up (verb)
become chocked with silt	establish as valid or genuine
	become or cause to become obstructed
	make a copy of (a computer file) especially for storage in another place as a security copy
	move backwards from a certain position
	give moral or psychological support, aid, or courage to